Preserve poetry venvs.

nix/configuration/roles/python/default.nix

@@ -32,6 +32,21 @@
           isort
           black
         ];
+
+        environment.persistence."/state" = lib.mkIf (!config.me.buildingIso) {
+          hideMounts = true;
+          users.talexander = {
+            directories = [
+              {
+                # Poetry virtual environments.
+                directory = ".cache/pypoetry";
+                user = "talexander";
+                group = "talexander";
+                mode = "0755";
+              }
+            ];
+          };
+        };
       }
     ]
   );